SIFP: Suppress warning Wstringop-truncation
    
    It is a false positive because we allocate 0 initialized function
    with size "str_len + 1". Result will be always NUL terminated.
    
    src/lib/sifp/sss_sifp_utils.c: In function ‘sss_sifp_strdup’:
    src/lib/sifp/sss_sifp_utils.c:62:5: warning: ‘strncpy’ output
        truncated before terminating nul copying as many bytes from
        a string as its length [-Wstringop-truncation]
         strncpy(result, str, str_len);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    src/lib/sifp/sss_sifp_utils.c:56:15: note: length computed here
         str_len = strlen(str);
                   ^~~~~~~~~~~
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>